It is known to fit such aircraft with actuators for eliminating or attenuating the aircraft vibration that results in particular from the alternating forces applied to the fuselage by the mechanism that provides the aircraft with lift and propulsion.
To this end, aircraft vibration is measured using at least one accelerometer delivering a vibration measurement signal, the measurement signal is processed by processor means including an algorithm recorded in an electronic card or in an on-board computer, so as to obtain a control signal that is applied to an actuator in order to generate forces that oppose the measured vibration.
The forces may result from the reciprocating movement of a mass mounted to move in translation relative to the structure of the aircraft. The mass is generally connected to the structure of the aircraft by a spring and is driven by a linear electromagnetic actuator; that type of antivibration actuator presents several drawbacks, and in particular:
i) poor efficiency which leads to high consumption of electricity, and also requires a powerful amplifier to be used on the control signal;
ii) the amplifier and the actuator present high mass; and
iii) the transfer function is not linear with control signal frequency, said transfer function presenting a peak at a resonant frequency.
It is also known to use a rotary actuator comprising unbalanced rotors (having unbalance weights) for producing forces by the centrifugal effect.
European patent EP 0 409 462 and U.S. Pat. No. 5,005,439 disclose a generator of inertial forces for canceling undesired vibration of an engine; the generator comprises a casing containing two pairs of unbalanced rotors presenting a common axis of rotation; each rotor in each pair of rotors is driven in rotation (inside the casing) by a respective variable speed motor; each pair of rotors comprises an outer rotor and an inner rotor that extends (in part) inside the outer rotor; the two rotors in a first pair of rotors are driven in a first direction of rotation, and the two rotors in the second pair of rotors are driven in a second direction of rotation opposite from the first direction of rotation; the four rotors present an unbalance weight (or eccentric mass) that is identical, and implemented in the form of a cylindrical shell or a sector of a plate; the frequency of the centrifugal inertial force of the generator is modified by varying the (common) speed of rotation of the rotors; the amplitude of the inertial force for each pair of rotors is modified by varying the angular offset between the unbalance weights of the rotors in the pair of rotors in question; the direction of the centrifugal inertial force of the generator is controlled by controlling the phase difference between the two pairs of rotors.
Adjusting those operating parameters requires the relative angular position of each rotor to be measured and adjusted continuously.
The unbalance weights of the four rotors are either centered in a plane that is orthogonal to the common axis of rotation when the rotors form “interleaved” shells, or else they are disposed on either side of and at a short distance from said plane, when juxtaposed plates and/or sectors are used.
Such a generator is also heavy and bulky.